Sensor devices and methods for use in sensing current through a conductor

ABSTRACT

A utility meter and related methods are disclosed. The utility meter includes a sensor device positioned around a conductor to sense current flowing through the conductor. The sensor device includes a non-magnetic substrate, a coil comprising a plurality of turns wound about the substrate, and a dielectric material having a dielectric constant and positioned between the coil and the conductor. The utility meter also includes a meter control board in communication with the sensor device to determine an amount of electricity transmitted through the conductor from the power source to the user over time. The dielectric constant of the dielectric material is selected to reduce a capacitive coupling between the coil and the conductor and to reduce a sensitivity of the sensor device such that the meter control board comprises only one calibration coefficient for calibrating the sensor device over a current range.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application, which claims thebenefit of U.S. patent application Ser. No. 13/229,038 filed on Sep. 9,2011, entitled “Sensor Devices and Methods for Use in Sensing CurrentThrough a Conductor”, the disclosure of which is hereby incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION

The field of the invention relates generally to sensor devices andmethods and, more particularly, sensing current through a conductor.

At least some known utility meters are used to measure electricitysupplied from a power source to a user. To enable an amount of energysupplied to a user to be accurately measured, utility meters ofteninclude one or more sensor devices to sense current flowing through aconductor between the power source and the user. When included in autility meter, the sensor device is intended to function accurately overan operating range of voltages and/or currents.

Various types of known current sensor devices are used in utilitymeters. For example, at least some known transformer sensor devicesinclude a magnet core with magnet wire wound thereon to sense currentflowing through a conductor. Current sensor devices includingtransformers, however, are generally known to be bulky and expensive.Current sensor devices with magnetic cores may be vulnerable to externalmagnetic fields. Exposure to external magnetic fields reduces theaccuracy of magnetic core current sensor devices, and in some cases theaccuracy may be reduced to the point where the current device registersonly as little as 8% of the current that the current device should besensing. Temperature cycles may also affect the magnetic core of currentsensors and cause magnetic drift which reduces the accuracy of thecurrent sensor.

Another example of a known current sensor device is a Rogowski coil.Rogowski coils include a coil and are generally smaller than transformersensor devices. However, Rogowski coils are known to provide onlylimited accuracy during low current and/or high current conditions overa range of voltages. As a result, during manufacturing, utility meterswith known Rogowski coils are often subjected to multiple calibrationprocesses to minimize the effects of these inaccuracies. Although theserepeated calibration processes may reduce the inaccuracies of suchsensor devices, the processes also increase manufacturing times andcosts of the utility meters.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a utility meter for use in transmitting electricalenergy from a power source to a user is provided. The utility meterincludes a sensor device positionable at least partially around aconductor to sense current flowing through the conductor and to output asignal representative of the sensed current. The sensor device includesa non-magnetic substrate, a coil comprising a plurality of turns woundabout the substrate where the coil defines an aperture through which theconductor is to be received, and a dielectric material having adielectric constant and positioned adjacent to the coil and at leastpartially within the aperture such that the dielectric material isbetween the coil and the conductor when the conductor is receivedthrough the aperture. The utility meter also includes a meter controlboard in communication with the sensor device to receive the signalrepresentative of the sensed current from the sensor device and todetermine an amount of electricity transmitted through the conductorfrom the power source to the user over time. The dielectric constant ofthe dielectric material is selected to reduce a capacitive couplingbetween the coil and the conductor and to consequently reduce asensitivity of the sensor device such that the meter control boardcomprises only one calibration coefficient for calibrating the sensordevice over a current range, and wherein the current range is about 2.0A to about 25,000 A.

In another embodiment, a method of fabricating a utility meter for usein transmitting electrical energy from a power source to a user isprovided. The method includes providing a sensor device positionable atleast partially around a conductor to sense current flowing through theconductor and to output a signal representative of the sensed current.Providing the sensor device includes forming a coil comprising aplurality of turns wound about a non-magnetic substrate where the coildefines an aperture through which the conductor is to be received, andpositioning a dielectric adjacent to the coil and at least partiallywithin the aperture such that the dielectric material is between thecoil and the conductor when the conductor is received through theaperture. The method also includes connecting a meter control board withthe sensor device to receive the signal representative of the sensedcurrent from the sensor device and to determine an amount of electricitytransmitted through the conductor from the power source to the user overtime, and selecting the dielectric material such that a dielectricconstant of the dielectric material reduces a capacitive couplingbetween the coil and the conductor and consequently reduces asensitivity of the sensor device such that the meter control boardcomprises only one calibration coefficient for calibrating the sensordevice over a current range where the current range is about 2.0 A toabout 25,000 A.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary utility meter including anexemplary sensor device.

FIG. 2 is a partially disassembled view of the sensor device shown inFIG. 1.

FIG. 3 is a perspective view of the sensor device shown in FIG. 1.

FIG. 4 is a plan view of the sensor device shown in FIG. 1.

FIG. 5 is a perspective view of an exemplary substrate and coil usedwith the sensor device shown in FIG. 1.

FIG. 6 is a cross-sectional view of an exemplary bobbin that may be usedwith the sensor device shown in FIG. 1.

FIG. 7 is a circuit diagram of an exemplary coil and shields that may beused with the sensor device shown in FIG. 1.

FIG. 8 is a perspective view of an exemplary sensor device includingfour lead wires.

FIG. 9 is a circuit diagram of an exemplary coil and shields that may beused with the sensor device shown in FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a block diagram of an exemplary utility meter 10. Inthe exemplary embodiment, utility meter 10 includes a sensor device 12,a conductor 14, and a meter control board 17 coupled to sensor device12. Conductor 14 may include a bus bar, multi-strand wire, single-strandwire, cable, or other suitable conductor to transmit electricity from apower source to a power user. The power source may include, withoutlimitation, an electrical grid and/or a power generator system, such asa gas turbine engine, a hydroelectric turbine, a wind turbine, a solarpanel, and/or another suitable generation and/or transmission system.The power source may also include a smart-grid in communication withmeter control board 17. A user may include, without limitation, aresidential user, a commercial user and/or any other user of electricityat any level. Sensor device 12 is coupled to conductor 14 to sensecurrent flowing through conductor 14. Sensor device 12 provides a signalrepresentative of sensed current to meter control board 17. Based on thesignal received from sensor device 12, meter control board 17 determinesan amount of electricity transmitted through conductor 14 from the powersource to the user over time.

Because a charge may be incurred for electricity transferred from thepower source to the user, it is desirable that sensor device 12 ishighly accurate to ensure the user is charged substantially only forelectricity received, rather than being charged for substantially allthe electricity transmitted to the user by the operator of the powersource.

In this exemplary embodiment, utility meter 10 further includesconductors 15 and 16 and another sensor device 12 coupled to conductor15. It should be appreciated that any number of conductors and/or sensordevices (e.g., one, three, six, etc.) may be used in other utility meterembodiments. Moreover, it should be appreciated that sensor device 12 isnot limited to only being used within utility meter 10, but may beutilized in virtually any application to sense current through aconductor, such as power generation applications, utility applications,automotive applications, appliance applications, telecommunicationapplications, etc.

FIG. 2 is a partially disassembled view of exemplary sensor device 12.In the exemplary embodiment, sensor device 12 includes a substrate 102,a coil 104 including a plurality of turns wound about substrate 102, anda dielectric material 108. Coil 104 includes an aperture 110 definedtherein, which is structured (e.g., by size, orientation, and/or shape,etc.) to receive conductor 14 therein. Dielectric material 108 ispositioned adjacent to coil 104 and at least partially within aperture110. More specifically, in this embodiment, dielectric material 108 ispositioned at least partially between coil 104 and conductor 14, whenconductor 14 is positioned through aperture 110.

Dielectric material 108 may include one or more dielectric materialshaving a variety of characteristics configured in a variety of ways. Forexample, dielectric material 108 may have a dielectric constant equal toor greater than about 3.0 at about 10-1000 Hz. In some embodiments, thedielectric constant may be greater than about 3.5, about 4.0, about 5.0,about 8.0, about 12.0, about 17.0 and/or any other suitable dielectricconstant. In one exemplary embodiment, the dielectric constant ofdielectric material 108 may be approximately equal to about 3.5. Inanother exemplary embodiment, the dielectric constant of dielectricmaterial 108 may be approximately equal to about 6.0.

Further, dielectric material 108 has at least one thickness, and mayhave various thicknesses. In the exemplary embodiment, dielectricmaterial 108 positioned adjacent to coil 104 and at least partiallywithin aperture 110 has a thickness of about 3.0 millimeters. Also, inthe same embodiment, dielectric material 108 positioned adjacent to coil104 but opposite aperture 110 has a thickness of about 1.2 millimeters.It should be appreciated that dielectric material 108 may have anythickness or thicknesses, that enables sensor device 12 to function asdescribed herein. Generally, thickness of dielectric material 108 isselected, at least partially based on the dielectric constant ofdielectric material 108, the proximity of coil 104 to one or moreconductors 14, 15 and 16, and/or space available in an intendedenvironment for installation of the sensor device, etc. In some exampleembodiments, the thickness of dielectric material 108 may range fromabout 1.0 millimeter to about 3.0 centimeters, or greater in still otherembodiments.

In the exemplary embodiment, dielectric material 108 may be fabricatedfrom one or more of several types of material, such as, withoutlimitation, plastic materials, thermoplastic materials, thermosetmaterials, ceramic materials, metallic materials, wood materials, claymaterials, organic materials, any mixture thereof, and/or othermaterials suitable to perform as described herein. In the exemplaryembodiment of FIG. 2, dielectric material 108 includes a PBTthermoplastics material commercially available from a Valox® family ofmaterials. In various embodiments, dielectric material 108 includes oneor more of, without limitation, Kapton® tape, a polyvinylidene fluoride(PVDF) material, a room temperature vulcanized silicone (RTV) polymer, aPBT thermoplastics material commercially available from a Valox® familyof materials (e.g., Valox® 365 or Valox® V9561), a polyethyleneterephthalate (PET) thermoplastic material from the Rynite® family ofmaterials, a PPS thermoplastic material commercially available from theRyton® family of materials, a PPS thermoplastic material commerciallyavailable from the Primef® family of materials, a nylon thermoplasticmaterial commercially available from the Zytel®, Stanyl®, or RTP®families of materials, a LCP thermoplastic material (e.g., Sumitomo®E5008L or E4008L materials), etc. One or more types of dielectricmaterial 108 may be selected based on dielectric constant, suitabilityfor one or more manufacturing techniques, dimensional stability, cost,moldability, workability, rigidity, and/or other characteristic of thematerial(s). In at least one example, dielectric material 108 isselected at least partially based on the variability of its dielectricconstant over temperature.

FIG. 3 is a perspective view of sensor device 12 (shown as assembled)with conductor 14 extending through aperture 110. As described above,sensor device 12 senses current flow through conductor 14. Specifically,when current flows through conductor 14, a current is induced in coil104. The amount of current induced in coil 104 is representative of theamount of current flowing through conductor 14. When sensor device 12 ispositioned around conductor 14, coil 104 is spaced a distance fromconductor 14. Accordingly, capacitance exists between coil 104 andconductor 14. The capacitance may affect the accuracy of sensor device12 at different operating voltages (e.g., a range from about 30V toabout 277V). In the exemplary embodiment, dielectric material 108 ispositioned within at least a portion of an air-gap 106 defined betweencoil 104 and conductor 14. As a result, dielectric material 108 affectsand/or facilitates a reduction of the capacitance between coil 104 andconductor 14, while permitting coil 104 and conductor 14 to remain inclose proximity.

The reduction in capacitance enables sensor device 12 to sense currentflowing through conductor 14 with improved accuracy, as compared toknown Rogowski coils or other air-gap coils. More specifically, byreducing capacitance coupling between coil 104 and conductor 14, thesensitivity to operating voltage is reduced. As a result, consistentcurrent sensing is provided at different operating voltages across arange of different currents, including high and low currents.Accordingly, when sensor device 12 is included in utility meter 10, oneor more processes necessary for calibrating known sensor devices may beomitted. Specifically, in the exemplary embodiment, the consistency ofsensor device 12 to accurately detect current across different operatingvoltages may permit meter control board 17 to use only one calibrationcoefficient for a plurality of operating voltages, as compared to knownutility meters, which require multiple calibration coefficients for useat different voltages. Moreover, the reduction in capacitance betweencoil 104 and conductor 14 not only facilitates reducing and/orsimplifying the calibration processes, but also facilitates reducingmanufacturing cost, resources, and/or time with at least the same andoften improved accuracy across operating voltage/current ranges.

As shown in FIG. 3, in this exemplary embodiment, sensor device 12includes an enclosure 112. Enclosure 112 may be formed from a variety ofmaterials and/or through a variety of fabrication processes. In theexemplary embodiment, enclosure 112 includes substantially onlydielectric material 108, such that dielectric material 108 is positionedabout coil 104, opposite aperture 110. As such, when used within utilitymeter 10 having three-phase conductors 14, 15, and 16, sensor device 12may be positioned about conductors 14 and proximate to at least oneother conductor 15 (as shown in FIG. 1), and potentially proximate toconductor 16. Similar to the interaction between coil 104 and conductor14, a capacitance exists between coil 104 and conductor 15, which mayadversely affect and/or degrade the accuracy of sensor device 12. Due tothe position of dielectric material 108 opposite aperture 110,dielectric material 108 is positioned between coil 104 and adjacentconductor 15. Accordingly, dielectric material 108 is further providedto reduce capacitance between coil 104 and conductor 15. In this manner,sensor device 12 may provide improved accuracy when used in utilitymeter 10 having multiple conductors and/or when used in close proximityto one or more other conductors, as compared to known air-gap coils.

In some embodiments, enclosure 112 may include one or more materials inaddition to dielectric material 108, such as non-dielectric materials ordielectric materials that have different characteristics. In oneembodiment, enclosure 112 includes dielectric material 108 and anadditive material, which is provided to support dielectric material 108in one or more locations relative to coil 104 to enable it to perform asdescribed herein. The additive material may include plastic materials,thermoplastic materials, thermoset materials, ceramic materials,metallic materials, wood materials, clay materials, organic materials,any mixture thereof, and/or other suitable materials. The additivematerial may be selected based on manufacturing techniques, dimensionalstability, cost, moldability, workability, rigidity, and/or othercharacteristics of the material, etc. In such embodiments, whendielectric material 108 is a higher cost material (as compared to theadditive material), the inclusion of an additive material may reduce theoverall cost of sensor device 12. Further, one or more additivematerials may be used to perform one or more additional functions, suchas supporting dielectric material 108, protecting and/or insulating coil104, etc. As should be apparent, the additive material may be used aspart of enclosure 112 in various embodiments. In the exemplaryembodiment, however, an additive material is omitted, as enclosure 112substantially only includes dielectric material 108.

Enclosure 112 may be fabricated from the dielectric material, formedintegrally from dielectric material 108 and at least one additivematerial, or assembled from separate dielectric material(s) 108 andadditive material(s). Enclosure 112 and/or dielectric material 108 maybe fabricated using one or more injection molding processes and/or othersuitable fabrication processes. In the exemplary embodiment, enclosure112 is constructed via a single injection molding process, in whichdielectric material 108 is injected into a mold structured to formenclosure 112.

Alternatively, enclosure 112 may be constructed from a multi-stageinjection molding process. In a multi-stage process, an additivematerial is molded into a specific shape through an initial moldingprocess. Subsequently, the molded additive material is positioned withina mold, and dielectric material 108 is injected into the mold.Dielectric material 108 flows into voids defined between the mold and/orthe additive material, to form enclosure 112 from dielectric material108 and additive material. In various embodiments, a multi-stage moldingprocess may permit a relatively high-cost dielectric material to bespecifically positioned relative to coils 104 such that desiredperformance as described herein is achieved, while still permittingother portions of enclosure 112 to be constructed from one or morerelatively low cost materials.

It should be appreciated that enclosure 112 may be constructed by otherfabrication techniques to provide dielectric material 108 throughout orat desired positions relative to coil 104 and/or conductor 14. In oneexample, dielectric material 108 is constructed separately from anadditive material, and subsequently transformed and/or constructed withthe additive material to form enclosure 112. In yet another example, atubular dielectric material may be inserted into an aperture formed byan additive material to form enclosure 112.

In the exemplary embodiment, enclosure 112 includes a mount 116 thatdefines aperture 110. When conductor 14 is received in aperture 110 (asshown in FIG. 3), air-gap 106 is formed between mount 116 and conductor14. Simultaneously, a friction fit is created between mount 116 andconductor 14. Mount 116 may include dielectric material 108 and/oranother material. It should be appreciated that mount 116 may be formedin a variety of different shapes that are designed to receive and/orcouple to various types, shapes, and/or orientations of conductors. Inat least one embodiment, mount 116 defines an aperture that isstructured to form a friction fit with a rectangular-shaped bus barconductor.

Referring again to FIG. 2, enclosure 112 includes a first portion 118and a second portion 120. First portion 118 is releasably coupled tosecond portion 120 such that substrate 102 and coil 104 aresubstantially enclosed therein. Specifically, when assembled, as shownin FIG. 3, first portion 118 is coupled to second portion 120 through atleast one ship-lap joint to form enclosure 112. It should be appreciatedthat first portion 118 and second portion 120 may be coupled togetherthrough a variety of different methods, including, without limitation,one or more butt joints, screw joints, hinge joints, tab-slotarrangements, tongue-and-groove arrangements, fasteners, etc. Whileenclosure 112 has generally toroidal shape, as shown in FIG. 3, itshould be appreciated that other enclosure embodiments may define anyshape and/or size, that is sized and/or operates to at least partiallyenclose substrate 102, coil 104 and/or shields, and that enablesdielectric material 108 to perform as described herein.

Further, in the exemplary embodiment, the thickness of dielectricmaterial 108 varies throughout enclosure 112. The ship-lap joint betweenfirst portion 118 and second portion 120 provides an overlap of firstportion 118 and second portion 120. Specifically, in this exemplaryembodiment, first portion 118 and second portion 120 each have athickness of about 1.2 millimeters at aperture 110. When the firstportion 118 and the second portion 120 are assembled, first portion 118and second portion 120 at least partially overlap at the ship-lap joint(along aperture 110) to create a total thickness of about 2.4millimeters. Moreover, in this exemplary embodiment, first portion 118and second portion 120 are structured such that the total thicknessabout the outside of enclosure 112 at a minor ship-lap joint (oppositeaperture 110) is less than about 1.2 millimeters. It should beappreciated that various methods of forming enclosure 112 may be used toprovide one or more different thicknesses of enclosure 112 and/ordielectric material 108.

In various other embodiments, the thickness of enclosure 112 and/ordielectric material 108 may be between about 0.5 millimeters and about3.0 centimeters. In some embodiments, one or more thicknesses ofenclosure 112 and/or dielectric material 108 are between about 1.0millimeters and 6.0 millimeters. Further, in various embodiments, one ormore thicknesses of enclosure 112 and/or dielectric material 108 arebetween about 1.0 millimeters and 4.0 millimeters. It should beappreciated that enclosure 112 and/or dielectric material 108 may havedifferent thickness in other embodiments, potentially based on a methodof assembly/fabrication, the characteristic(s) of a selected dielectricmaterial, and/or desired performance characteristic(s). Further, othershapes, sizes, and/or joints for enclosure 112 may be used to at leastpartially enclosure coil 104, while positioning dielectric material 108relative to coil 104 to perform consistent with one or more aspects ofthe present disclosure.

In the exemplary embodiment, coil 104 includes an exemplary Rogowskicoil. It should be appreciated, however, that sensor device 12 mayinclude a coil other than a Rogowski coil. Further, aspects of thepresent disclosure are not limited to only being used with a Rogowskicoil as described and illustrated herein.

FIG. 5 is a perspective view of substrate 102 and coil 104 separatedfrom enclosure 112. In the exemplary embodiment, substrate 102 includessix bobbins 124, 126, 128, 130, 132, and 134 (collectively referred toas bobbins 124-134). Each bobbin 124-134 has a substantially circularcross-section, and more particular, is a right cylinder that includesflanges 135 at opposite ends that retain coil 104. In other embodiments,substrate 102 may have a different number, shape, and/or size ofbobbins. For example, substrate 102 may include five bobbins, eightbobbins, ten bobbins, thirty bobbins, or another even or odd number ofbobbins. Further, substrate 102 may include bobbins having a differentshape, and/or an ovular cross-section, an elliptical cross-section, orrectangular cross-section, etc. In still other embodiments, substrate102 may include a different structure for supporting coil 104, inaddition to or other than flanges 135. In at least one embodiment, coil104 is sufficient rigid to omit substrate 102.

In the exemplary embodiment, bobbins 124-134 are coupled together viahinged joints 137. More specifically, bobbins 124 and 126 are hingedlycoupled to permit pivotal movement therebetween. In various embodiments,bobbins 124-134 may be linearly aligned to enable efficient winding ofcoil 104 and/or pivoted relative to one another to form a substantiallycircular shape, as illustrated in FIG. 5.

Each of bobbins 124-134 of substrate 102 is a non-magnetic structure,such that bobbins 124-134 are constructed from one or more non-magneticmaterials, including, for example, thermoplastic material, ceramicmaterial, wood, material, or other kinds of suitable material(s). Inthis exemplary embodiment, each of bobbins 124-134 is fabricated from adielectric material, potentially consistent with dielectric material108. By use of a non-magnet substrate 102, cost savings may be realizedover known sensor devices that include one or more magnetic cores.Moreover, in the exemplary embodiment, substrate 102 is shaped and/orsized to provide improved mounting within utility meter 10 and/or to ameter control board 17, as compared to known sensor devices that includebulky magnetic cores. Further, in this exemplary embodiment, bobbins124-134 are formed separate from enclosure 112. It should beappreciated, however, that bobbins 124-134 may be formed integrally withand/or form one or more portions of enclosure 112 in other sensor deviceembodiments.

In the exemplary embodiment, coil 104 is wound multiple turns on eachbobbin 124-134. More specifically, in the exemplary embodiment, coil 104includes a single magnet wire that enables coil 104 to be wound frombobbin 124 to bobbin 134 with several turns on each bobbin 124-134, andthen wound back to bobbin 124 with additional turns on each bobbin124-134. It should be appreciated that, in other embodiments, otherdifferent winding patterns on bobbins 124-134 may be used. Consistentwith the above winding pattern across bobbins 124-134, a first end and asecond end of coil 104 terminates at bobbin 124. The first end of coil104 is terminated at lead wire 136, and the second end of coil 104 isterminated at lead wire 138, as shown in FIG. 7, described furtherbelow.

In addition to coil 104, in the exemplary embodiment, one or moreshields are applied to substrate 102. Specifically, FIG. 6 illustrates apartial cross-sectional view of sensor device 12 at bobbin 124. In theexemplary embodiment, bobbin 124 includes a first shield 140 and asecond shield 142. First shield 140 is positioned between bobbin 124 andcoil 104. Second shield 142 is positioned adjacent to coil 104 andopposite from first shield 140, such that coil 104 is positioned betweenfirst shield 140 and second shield 142. Each bobbin 124-134 includessubstantially the same shield-coil-shield pattern as shown in FIG. 6. Inother embodiments, bobbins 124-134 may include other winding patterns,including winding patterns, in which the winding pattern varies from onebobbin to another bobbin.

In the exemplary embodiment, each shield 140 and 142 provides a Faradayshield. More specifically, in this exemplary embodiment, first andsecond shields 140 and 142 behave substantially consistent with aFaraday cage, in order to facilitate reducing common mode noise on thesensor device 12 and/or to provide a low-pass filter for high frequencynoise filtering. As a result, first and second shield 140 and 142facilitate improved performance in the context of one or more industrystandards for electromagnetic interface (EMI) and/or electromagneticcompatibility (EMC).

During fabrication, a plurality of turns of a magnet wire are wound oneach bobbin 124-134 from bobbin 124 to bobbin 134 to form first shield140. Coil 104 is then wound from bobbin 124 to bobbin 134 and back tobobbin 124 as described above. Subsequently, the magnet wire of firstshield 140 is wound from bobbin 134 back to bobbin 124 with a pluralityof turns on each bobbin 124-134 to form second shield 142. As such, inthe exemplary embodiment, first shield 140 and second shield 142 areformed from a single magnet wire. The single magnet wire includes twoends, which may be terminated together, coupled to lead wire 138, and/orcoupled to one or more additional lead wires, as described below. Itshould be appreciated that first shield 140 and second shield 142 mayinclude any suitable materials, such as, without limitation, copper,aluminum or other nonferrous conducting material. More generally, theshielding material may be formed as a sheet, a tape, a wire, a sprayand/or any other form that enables bobbins 124-134 to include shields140 and 142. As such, application of shields 140 and/or 142 may beformed, without limitation, via winding, wrapping, and/or spraying, forexample. In various embodiments, first and second shield 140 and 142 maybe formed separately from coil 104 and subsequently applied to coil 104.

Referring again to FIG. 5, sensor device 12 includes three lead wires136, 138, and 144 extending therefrom. FIG. 7 illustrates a circuitdiagram of the coupling of lead wires 136, 138, and 144. Specifically,in the exemplary embodiment, first and second shields 140 and 142 areformed from a single magnet wire, with each end coupled together andcoupled to lead wire 144. Further, the first end of coil 104 (formedfrom a single magnet wire) is coupled to lead wire 136, and a second endof coil 104 is coupled to lead wire 138. As shown in FIG. 5, lead wires136, 138, and 140 extend from enclosure 112 and form a twisted wire set.As such, lead wire 144 behaves as a low pass filter element to inhibitnoise from first shield 140 and/or second shield 142 from being injectedinto a return path of the current signal provided by sensor device 12.The twisted wire set has a length of at least about 0.25 inches. Inother embodiments, twisted wire set may have a length of at least about1.0 inches, or a length of at least about 3.0 inches. In furtherembodiments, twisted wire set may have a length of at least about 6.0inches. It should be appreciated that other lengths of lead wires and/ortwisted wire sets may be employed in other sensor device embodiments,possibly based on the performance of the lead wire and/or twisted wireset to function as a filter to inhibit the injection of noise into acurrent signal transmitted from sensor device 12.

FIGS. 8-9 illustrates another exemplary sensor device 200. In theexemplary embodiment, sensor device 200 includes a coil 204 and firstand second shields 240 and 242, which are substantially consistent withcoil 104 and shields 140 and 142 described above. Sensor device 200,however, includes four lead wires 236, 238, 244, and 245. Specifically,each end of the magnet wire forming first shield 240 and second shield242 are coupled to separate lead wires 244 and 245 to create a filterelement. Additionally, in this exemplary embodiment, two lead wires 236and 238 coupled to coil 204. As illustrated in FIG. 8, lead wires 236,238, 244, and 245 form a twisted wire set, which functions substantiallyconsistent with the twisted wire set described above with reference toFIG. 5.

When coupled to meter control board 17, each lead wire 244 and 245 maybe coupled together and coupled to lead wire 238. In some embodiments,twisted lead wires 244 and 245 may behave as a filter element.Additionally, or alternatively, a filter element may be coupled betweenlead wires 244 and 245 and lead wire 238. Such filter elements mayinclude, without limitation, a resistor-capacitor circuit, aninductor-capacitor circuit, a resistor-inductor circuit, and/or aresistor-inductor-capacitor circuit.

Referring again to FIGS. 3 and 7, in yet another embodiment, each end ofthe magnet wire forming shields 140 and 142 may be coupled together andcoupled to lead wire 138 (i.e., one end of coil 104), rather than aseparate lead wire 144 In such an exemplary embodiment, sensor device 12may include lead wires 136 and 138, while omitting lead wire 144,thereby providing a two-wire sensor device 12. In the exemplaryembodiment, some noise from first shield 140 and/or second shield 142may be injected into the return path of a current signal provided fromsensor device 12, while providing sufficient accuracy and/orrepeatability for a desired operating environment. In still otherembodiments, lead wires may be omitted from a sensor device embodimentto provide for mounting on a circuit board, such as meter control board17. In such an embodiment, a filter element may be provided by traces onmeter control board 17, with a sufficient length to perform as describedabove with reference to lead wire 144. Additionally, or alternatively,filter element may include a resistor-capacitor circuit, aninductor-capacitor circuit, a resistor-inductor circuit, and/or aresistor-inductor-capacitor circuit, to inhibit noise from first shield140 and/or second shield 142 from being injected into a return path forthe current signal provided by sensor device 12.

In the exemplary embodiment, sensor device 12 is operational betweenabout 10 Hz to about 1000 Hz, and is substantially immune to signalsoutside this range. More specifically, conductor 14 may act as anantenna to pick up radio frequency (RF) signals and re-radiate theunwanted noise to sensor device 12. First and second shield 140 and 142perform as a low-pass filter to inhibit injection of noise signals toprovide a high signal-to-noise-ratio (SNR) output. More particularly,first and second shields 140 and 142 reject re-radiated RF signal(and/or other noise signals) to provide a high SNR for the output ofsensor device 12 when sensing low current through conductor 14. Byreducing the effect of noise on current signals, the effective currentsensing range of sensor device 12, within applicable standards, isbroader, as compared to known sensor devices. In the exemplaryembodiment, first and second shields 140 and 142 may permit one or moreadditional filter elements (for low and/or high current performance) tobe omitted.

Moreover, first and second shields 140 and 142 substantially inhibit EMIfrom affecting the accuracy of sensor device 12. More specifically,first and second shields 140 and 142 facilitate inhibiting the effectsof EMI sources positioned adjacent to sensor device 12, such as adjacentelectronics and/or devices intended to interfere with the accuracy ofsensor device 12 and/or utility meter 10. Additionally, by omitting amagnetic core, as compared to known sensors, sensor device 12 providesenhanced immunity to EMI affects on accuracy. As such, sensor device 12provides a more robust and/or accurate current sensor device, ascompared to other known sensor devices in the presence of one or moreEMI sources.

Accuracy of sensor device 12 may be understood as a percentage of theactual value of current flowing through conductor 14. In the exemplaryembodiment, sensor device 12 performs within about ±0.2% of the actualvalue in the range between about 2 amps and about 200 amps. Morespecifically, sensor device 12 performs within Class 0.2, 0.1 A to 200 Aat an operating voltage of between about 60V and about 600V, morespecifically at about 240V, within an accuracy of 0.2%. It should beappreciated that sensor device 12 consistent with one or more aspects ofthe present disclosure may conform to one or more different accuracystandards at different operating currents/voltages, possibly dependingon the intended application and/or one or more accuracy requirementsassociated with the intended application.

Various methods are described herein for fabricating a sensor device forsensing current through a conductor. While these methods are describedbelow with reference to sensor device 12, it should be understood thatthe methods are not limited to sensor device 12 and may be utilized tofabricate other sensor device embodiments. Likewise, sensor device 12and sensor device 200 may be fabricated from methods other than thosedescribed below.

One exemplary method of fabricating sensor device 12 for sensing currentthrough a conductor 14 includes providing coil 104 with a plurality ofturns about non-magnetic substrate 102 and positioning dielectricmaterial 108 adjacent to coil 104, such that when conductor 14 isdisposed within aperture 110 defined by sensor device 12, dielectricmaterial 108 is positioned between conductor 14 and coil 104. In severalembodiments, the exemplary method may include at least partially and/orsubstantially enclosing coil 104 and/or substrate 102 within enclosure112.

Another exemplary method of fabricating sensor device 12 for sensingcurrent through conductor 14 includes providing Rogowski coil 104 and atleast partially enclosing Rogowski coil 104 within dielectric material108 such that, when Rogowski coil 104 is disposed about conductor 14,dielectric material 108 is disposed between Rogowski coil 104 and theconductor 14. Dielectric material 108 has a dielectric constant ofgreater than or equal to about 3.5. In several embodiments, theexemplary method may include assembling a first portion of an enclosureand a second portion of the enclosure with the Rogowski coil disposedtherebetween to at least partially enclose the Rogowski coil. Theenclosure includes the dielectric material. Additionally, oralternatively, the exemplary method may include forming the Rogowskicoil on a substrate having a plurality of thermoplastic bobbins.Further, the exemplary method may include forming the plurality ofthermoplastic bobbins from a dielectric material.

Yet another exemplary method of fabricating a sensor device 12 forsensing current through a conductor 14 includes winding a first shieldof a magnet wire about each of a plurality of bobbins of a substrate,winding a coil about each of the plurality of bobbins of the substrate,and winding a second shield of magnet wire about each of the pluralityof bobbins of the substrate.

Referring to sensor device 12 of FIG. 3, for example, the exemplarymethod may include coupling a first end and a second end of the magnetwire to a reference lead 144 of sensor device 12, coupling a first endof the coil to a first lead 136 of sensor device 12, and coupling asecond end of the coil to a second lead 138 of sensor device 12.Further, the exemplary method may include at least partially enclosingthe coil and the first and second shield within an enclosure, theenclosure comprising at least one dielectric material.

Another exemplary method of fabricating a sensor device 12 for sensingcurrent through a conductor 14 includes providing sensor device 12including non-magnetic substrate 102 defining aperture 110, coil 104having a plurality of coil turns about at least a portion ofnon-magnetic substrate 102, first shield 140 disposed between each ofsubstrate 102 and the plurality of coil turns, second shield 142disposed proximate to the plurality of coil turns, opposite first shield140. The exemplary method also includes coupling lead wire 144 to atleast one of first shield 140 and second shield 142, coupling lead wire136 to a first end of coil 104, coupling lead wire 138 to a second endof coil 104, and forming a twisted set of lead wires from lead wires136, 138 and 144.

In various embodiment, coupling lead wire 144 to at least one of firstshield 140 and second shield 142 includes coupling lead wire 144 to eachof the first shield 140 and second shield 142. In other embodiments,coupling lead wire to at least one of first shield and second shieldincludes coupling lead wire 244 to first shield 140 and coupling a leadwire 245 to second shield 142.

As shown in FIG. 5, coil 104 wraps around substrate 102 in the form ofbobbins 124-134. In the exemplary embodiment, each bobbin 124-134 istoroidal and includes a circular area around which coil 104 is wrapped.The core of each bobbin 124-134 is an air core. Unlike the previouslydisclosed magnetic core current sensor devices, the air core of coil 104does not become saturated. Tests have shown that the disclosed air corecoil 104 is accurate at ±0.4% from 10 milliamperes to 25,000 amperes. Atlower currents, i.e., less than 1,000 Amps, the accuracy of sensordevice 12 is ±0.2%, while at higher currents, i.e., greater than 10,000Amps, the accuracy lowers to ±0.4%. At those higher currents, conductors14, 15, and 16 interact with each other and function as parallel platecapacitors, affecting the accuracy of sensor device 12. Sensor device 12is an inductor with no core to saturate; therefore, sensor device 12 canwork continuously as an inductor without the possibility of saturationor oversaturation.

As an inductor with an air core, sensor device 12 is voltageindependent. Whereas a traditional current transformer may burn out athigh voltages, sensor device 12 is able to read the current throughconductor 14 independent of what voltage is passing through conductor14. Voltage does not affect the operation of coil 104. Voltage is alsonot measured by sensor device 12 and rather is measured at a differentlocation in the power delivery system.

Although in the exemplary embodiment, sensor device 12 is described asbeing operational between about 10 Hz to about 1000 Hz, it should beappreciated that the air core enables sensor device 12 to operateoutside of that range as well. It should also be appreciated thatutility meter 10, may include multiple sensor devices 12 measuringmultiple different conductors. For example, in another exemplary utilitymeter 10, conductors 14, 15, and 16 may each be enclosed by a differentsensor device 12. One or more of the above described embodiments providea highly-accurate sensor device. More specifically, the sensor devices,utility meters, and methods described herein may provide ahighly-accurate sensor device that provides an expanded operating rangewith reduced calibration requirements over known coil sensors. Forexample, the disclosed dielectric material may provide reducedcapacitance between a coil and one or more conductors, thereby providingimproved accuracy across a range of currents and/or voltages. Theimproved accuracy may be realized with fewer calibration processesduring manufacturing, resulting in reduced manufacturing cost and/ortime. In another example, the disclosed shielding techniques provideimproved rejection of EMI, originating from other electronics and/ortampering devices.

Although specific features of various embodiments of the invention maybe shown in some drawings and not in others, this is for convenienceonly. In accordance with the principles of the invention, any feature ofa drawing may be referenced and/or claimed in combination with anyfeature of any other drawing.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal language of the claims.

What is claimed is:
 1. A utility meter for use in transmittingelectrical energy from a power source to a user, said utility metercomprising: a sensor device positionable at least partially around aconductor to sense current flowing through said conductor and to outputa signal representative of said sensed current, said sensor devicecomprising: a non-magnetic substrate; a coil comprising a plurality ofturns wound about said substrate, said coil defining an aperture throughwhich said conductor is to be received; and a dielectric material havinga dielectric constant and positioned adjacent to said coil and at leastpartially within said aperture such that said dielectric material isbetween said coil and said conductor when said conductor is receivedthrough said aperture; and a meter control board in communication withsaid sensor device to receive said signal representative of said sensedcurrent from said sensor device and to determine an amount ofelectricity transmitted through said conductor from the power source tothe user over time; wherein said dielectric constant of said dielectricmaterial is selected to reduce a capacitive coupling between said coiland said conductor and to consequently reduce a sensitivity of saidsensor device such that said meter control board comprises only onecalibration coefficient for calibrating said sensor device over acurrent range; and wherein said current range is about 2.0 A to about25,000 A.
 2. The utility meter of claim 1, wherein said dielectricmaterial comprises at least one of a thermoplastic material and athermoset material.
 3. The utility meter of claim 2, wherein saiddielectric material comprises at least one of a polyethyleneterephthalate (PET) material and a polybutylene terephthalate (PBT)thermoplastic material.
 4. The utility meter of claim 1, wherein saidsubstrate comprises a plurality of bobbins, at least one of saidplurality of turns is wound about each of said plurality of bobbins. 5.The utility meter of claim 1, further comprising a mount positioned atleast partially within said aperture, said mount configured to support aconductor positioned in said aperture, and wherein said mount isfabricated at least partially from said dielectric material.
 6. Theutility meter of claim 5, further comprising an enclosure at leastpartially enclosing said substrate and said coil, said enclosurecomprising said mount.
 7. The utility meter of claim 1, wherein saiddielectric material encloses at least a portion of said coil and atleast a portion of said substrate.
 8. The utility meter of claim 7,wherein the sensor device comprises a mount forming a friction fit withsaid conductor, wherein said mount defines at least one air-gap betweensaid sensor device and said conductor, and wherein said mount comprisesat least a portion of said dielectric material.
 9. The utility meter ofclaim 1, wherein said sensor device is configured to sense currentthrough said conductor within about ±0.2% of an actual current throughsaid conductor in a current range between of about 2.0 Amps to about 320Amps.
 10. The utility meter of claim 1, wherein said sensor device isconfigured to sense current through said conductor within about ±0.5% ofan actual current through said conductor in a current range between ofabout 2.0 Amps to about 25,000 Amps.
 11. The utility meter of claim 8,wherein said substrate comprises a plurality of bobbins, wherein atleast one of said plurality of turns is disposed about each of saidplurality of bobbins and wherein each of said plurality of bobbinscomprise a thermoplastic material.
 12. The utility meter of claim 11,wherein said conductor includes one of a bus bar and a multi-strandconductor.
 13. The utility meter of claim 8, further comprising a secondsensor device positionable at least partially around a second conductorand in communication with said meter control board.
 14. The utilitymeter of claim 13, further comprising a third sensor device positionableat least partially around a third conductor and in communication withsaid meter control board.
 15. A method of fabricating a utility meterfor use in transmitting electrical energy from a power source to a user,said method comprising: providing a sensor device positionable at leastpartially around a conductor to sense current flowing through saidconductor and to output a signal representative of said sensed current,wherein providing said sensor device comprises: forming a coilcomprising a plurality of turns wound about a non-magnetic substrate,said coil defining an aperture through which said conductor is to bereceived; and positioning a dielectric adjacent to said coil and atleast partially within said aperture such that said dielectric materialis between said coil and said conductor when said conductor is receivedthrough said aperture; and connecting a meter control board with saidsensor device to receive said signal representative of said sensedcurrent from said sensor device and to determine an amount ofelectricity transmitted through said conductor from the power source tothe user over time; selecting said dielectric material such that adielectric constant of said dielectric material reduces a capacitivecoupling between said coil and said conductor and consequently reduces asensitivity of said sensor device such that said meter control boardcomprises only one calibration coefficient for calibrating said sensordevice over a current range; and wherein said current range is about 2.0A to about 25,000 A.
 16. The method of claim 15, wherein positioning thedielectric material adjacent to the coil includes at least partiallyenclosing the coil within an enclosure, said enclosure comprising thedielectric material.
 17. The method of claim 15, wherein forming thecoil includes winding at least one turn of the coil on each of aplurality of bobbins of the substrate.
 18. The method of claim 15,further comprising configuring said sensor device to sense currentthrough said conductor within about ±0.2% of an actual current throughsaid conductor in a current range between of about 2.0 Amps to about 320Amps.
 19. The method of claim 15, further comprising configuring saidsensor device to sense current through said conductor within about ±0.5%of an actual current through said conductor in a current range betweenof about 2.0 Amps to about 25,000 Amps.
 20. The method of claim 15,further comprising: positioning a second sensor device at leastpartially around a second conductor; and positioning a third sensordevice at least partially around a third conductor; wherein said secondsensor device and said third sensor device are connected with said metercontrol board.